A hydraulic excavator (or hydraulic shovel) includes a traveling body having left and right crawler mechanisms, a revolving body revolvably provided on the traveling body, and an excavator device provided at the front of the revolving body. As such a hydraulic excavator, a hydraulic excavator including a power supply unit having a battery and an inverter, an electric motor that drives in response to electricity from the power supply unit, a hydraulic pump driven by the electric motor, and a plurality of hydraulic motors and hydraulic cylinders that are activated in response to a hydraulic oil discharged from the hydraulic pump is known. The hydraulic excavator is configured such that the crawler mechanisms, the excavator device, and the like are activated by the hydraulic motors and hydraulic cylinders, thereby performing travel, excavation work, and the like.
Hydraulic actuators provided in such a hydraulic excavator include a traveling motor for activating the crawler mechanisms, a revolution motor for revolving the revolving body, a boom cylinder, an arm cylinder, a bucket cylinder, and a swing cylinder for activating an excavator device, a blade cylinder for moving a blade up and down, and the like. As a conventional hydraulic excavator, one equipped with a hydraulic drive unit configured such that a plurality of hydraulic pumps (including a pilot pump) are driven by one electric motor, and, using hydraulic oils discharged from these hydraulic pumps, a plurality of hydraulic actuators as described above are activated, and also a pilot pressure is generated, is known. In such a hydraulic drive unit, it is necessary to drive all the hydraulic pumps by one electric motor in order to achieve a pump discharge pressure corresponding to the maximum load pressure among all the hydraulic actuators. Therefore, it has often happened that the electric motor consumes extra energy.
Then, a hydraulic drive unit including two electric motors, and configured such that a traveling motor and hydraulic cylinders of an excavator device (boom cylinder, etc.) are activated using a hydraulic oil from a hydraulic pump driven by the first electric motor, and, using a hydraulic oil from a hydraulic pump driven by the second electric motor, a revolution motor and a blade cylinder are activated, and also a pilot pressure is generated, is also known (e.g., Japanese Patent No. 5096417B2). In such a hydraulic drive unit, it is possible that at the time of traveling and the activation of the excavator device only, the rotation speed (the number of rotations per unit time) of the second electric motor (electric motor for revolution, etc.) is suppressed low, while at the time of revolution and the activation of the blade only, the rotation speed of the first electric motor (electric motor for traveling, etc.) is suppressed low. As a result, the energy consumption of the two electric motors can be suppressed.